Functions required in fluid medium compression include the intake of a high volume of medium at low, typically ambient, pressure, compression of the medium into low volume and consequent higher pressure and issuance or outlet of the medium at such higher pressure. These functions are realized mechanically in known apparatus by a housing supporting a piston for movement in a compression chamber, inlet and outlet ports and suitable valving and control mechanism for operating the valves.
In a quite simple type of air pump, wide variations of which are known, a translatory piston defines a compression surface in which a one-way valve is supported. The valve is typically a flap member on the compression surface overlying an opening therein which extends through the piston into fluid communication with the housing intake port. On the piston compression stroke, the flap is maintained flush with the compression surface and functions therewith to compress air in the compression chamber. On the piston return stroke, the flap is opened by pressure differential, since the return stroke creates subambient pressure in the compression chamber, and ambient air flows from the housing intake port through the open flap valve into the compression chamber, readying the pump for the next compression stroke.
In the described apparatus, disadvantage exists in manufacture based on the need for attachment of the flap to the compression surface for movment, in pressure loss through the flap attachment structure and in need for replacement of the flap and/or its attachment structure in the course of usage.
Some effort is seen in the prior art which would avoid the foregoing disadvantages attending flap valve air pumps or like pumps having valved pistons. In U.S. Pat. No. 3,716,310 a fluid compressor includes a "dissociating" piston having a first compression surface-defining portion in the form of a truncated sphere and a second portion movable relative to the first portion to escape from sealed contiguity therewith and hence to place fluid flow passages of the second portion in communication with the compression chamber. Biasing means is included to sealingly mate the two piston portions. In the course of the return stroke in the '310 pump, it appears that inertia of the first portion causes it to lag and thus separate somewhat, overcoming the biasing means, from the positively-displaced second portion, whereby the compression chamber is replenished with ambient air. A point is reached at which the biasing means returns the two portions into mated relation, whereupon the compression stroke commences.
As in the first discussed generally known pump with flap valve, resilient means again is present in the '310 pump as an operative element in valving function and pumping constancy is dependent thereon, efficiency lessening as the resilient means wears. Pump assembly is relatively complex and resilient part wear and replacement are again present.